In recent years, display panels such as liquid crystal display panels are used for various types of electronic equipment. In particular, electronic equipment for mobile use, such as cellular phones, needs to narrow a frame region at the outer periphery of a display screen, i.e., needs to narrow the frame and, thereby, to reduce the size of the electronic equipment.
A liquid crystal display panel of an active matrix drive type includes an active matrix substrate and a counter substrate that are opposed to each other, and a liquid crystal layer sandwiched between the active matrix substrate and the counter substrate. The active matrix substrate includes, in a rectangular display region corresponding to the above-described display screen, a plurality of gate signal lines extending in parallel with one another and a plurality of source signal lines extending in parallel with one another in a direction orthogonal to the gate signal lines. The active matrix substrate has a terminal region on its surface projecting from the counter substrate.
In order to reduce the device size and the number of components, typical mobile electronic equipment including a display panel of an active matrix drive type has a so-called “three-side-free structure” in which a terminal region is disposed only on one of the four sides of an active matrix substrate and no terminal regions are disposed on the other three sides. On the active matrix substrate with the three-side-free structure, one gate control circuit is monolithically provided along each of the two opposed sides on which no terminal regions are disposed, one source control circuit is monolithically provided on one side on which the terminal region is disposed, and a driver integrated circuit (IC) connected to the gate control circuits and the source control circuit is mounted, for example. The gate control circuits are connected to gate signal lines. The source control circuit is connected to source signal lines. The source control circuit includes, for every three adjacent source signal lines, a demultiplexer circuit for splitting display source signals from video signal lines connected to the driver IC to color elements of RGB, an inspection circuit for inputting an inspection signal to the demultiplexer circuit, and a protection circuit for protecting the demultiplexer circuit, the inspection circuit, and thin film transistors (TFTs) provided in subpixels, which are minimum units of an image, for example.
For example, Patent Document 1 describes that a device substrate with a three-side-free structure can be designed such that an RGB switch circuit corresponding to the above-described demultiplexer circuit and a protection circuit for video signals are separated from each other and the pitch of arrangement in the protection circuit for video signals is smaller than that in the RGB switch circuit. This design is intended to reduce the size of the frame region of the substrate by creating a redundant region for disposing circuits, such as a protection circuit for general-purpose signals, and lines near both ends of components arranged in the protection circuit for video signal lines.